1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method. More particularly, the present invention relates to an image processing apparatus, an image processing method, and a program for correcting chromatic aberration caused by optical factors and suppressing color blur.
2. Description of the Related Art
Recent digital camcorders and digital cameras employ an image sensor having a large number of pixels to provide high-quality images. On the other hand, with pixel miniaturization and a decrease in lens size, color blur due to chromatic aberration is likely to occur because of wavelength-induced fluctuations in imaging position. Various methods have been proposed as techniques for suppressing color blur in a captured image.
For example, Japanese Patent Application Laid-Open No. 2000-076428 discusses a technique for suppressing color blur where a lens used for image capture is identified, relevant chromatic aberration information is read to generate correction parameters, and coordinates of target color signals are shifted based on the correction parameters.
However, the color blur characteristics intricately change with the image height position from the optical axis center to the pixel of interest, zoom lens position, diaphragm aperture diameter, and focus lens position. With the configuration discussed in Japanese Patent Application Laid-Open No. 2000-076428, in which the chromatic aberration information is read, chromatic aberration information is stored for each of the image height position, zoom lens position, diaphragm aperture diameter, focus lens position, and lens type.
Therefore, a large memory capacity is necessary to store these pieces of chromatic aberration information. Further, color blur may largely spread under certain photographing conditions, such as sunbeams streaming through leaves.
Another technique for suppressing color blur is proposed. With this technique, instead of reading prestored lens chromatic aberration information, an area in which color blur occurs is extracted and color blur suppression is applied to the area. For example, Japanese Patent Application Laid-Open No. 2007-195122 discusses a technique for suppressing color blur of image data based on gradient values of edges of the image data.
However, when suppressing color blur of image data based on gradient values of edges of the image data, a change in frequency characteristics of the image data input to the color blur suppression processor may cause insufficient or excessive color blur suppression possibly degrading the image quality. For example, when an image sensor is driven by a plurality of driving methods such as addition readout and non-addition readout, the frequency characteristics of image data generated by the image sensor change depending on the selected driving method.
When the method for driving the image sensor is changed from non-addition readout to addition readout, high-frequency components in the image data decrease by the addition average of pixel output signals. More specifically, even with an identical subject, an addition readout method may provide smaller gradient values of image data than a non-addition readout method.
Therefore, the amount of color blur suppression calculated based on gradient values of edges of image data has been different between the non-addition readout method and the addition readout method.